Radio paging systems that are in widespread use collect page messages from page requesting users and direct the page messages to remote receiving devices carried by page receiving users. It is desirable that the remote receivers reliably receive page messages, but due to a variety of factors including environmental conditions, every page message transmitted will not be received.
In some systems page messages are re-transmitted to improve the probability of their receipt. However, such retransmission of page messages burdens a valuable communication resource, namely, the transmission path bandwidth. Each re-transmission requires a portion of the transmission bandwidth which could be otherwise used for first transmission of other page messages. A second problem associated with re-transmission of page messages is that the person receiving the message does not know when the message was originally transmitted. It is misleading to receive an urgent message "call home" when the message was originally transmitted hours before receipt. While a time stamp can be transmitted with a message to indicate time of first transmission, this requires a significant portion of the bandwidth and typically is not necessary as most messages are received within minutes of first transmission. Accordingly, it is considered most efficient to simply inform the receiver of a missing message condition.
If the fact that one has missed a page message can be detected, the user can take corrective or remedial action. The prior referenced applications describe a missing page message detection system that indicates a missing page message to the page receiving user. The page receiving user can then recover the missing page message by telephone contact with the paging system.
In the missing page detection method described in the above referenced co-pending and commonly owned applications, each page message transmitted to a given receiver carries a consecutive message number. Each receiver interrogates message numbers as messages are received to detect and identify a missing page message as a gap in the message number sequence. The page message numbers also allow the receiver to distinguish new page messages from previously received page messages. This method reliably detects missing page messages, however, it requires receipt of a later page message. Page messages may be separated by hours, and sometimes days. Accordingly, a missing page message may not be detected until hours, and possibly days, after its transmission.
It would be desirable to provide a missing page message detection method which more quickly indicates a missing page message, without burdening the valuable transmission path resource.